The present invention relates to a pneumatic tire having a tread pattern designed so as to reduce stone biting without reducing the wet grip performance.
A pneumatic tire used for heavy duty vehicles, passenger cars and the like, are generally provided with straight or zig-zag longitudinal grooves extending in the circumferenial direction of the tire on the tread part from the view point of tire performances such as drainage, wear resistance and steering stability. It is unavoidable to run tires on rough roads in addition to paved roads. For instance, vehicles may be driven into a parking place in which broken stones are scattered thereon. In such a case, these longitudinal grooves are apt to bite pebbles or small broken stones. In addition, since the longitudinal grooves are generally formed in a constant groove width, the force of biting the stones is also strong. Accordingly, when the grooves once bite small stones, they are hard to be released and this stones causes cracking or damage of the bottom of the grooves and damage or breakage of the belt and the rubber inside the tire.
As a countermeasure against stone-biting and in order to prevent the stone-biting or to facilitate the release of small stones bitten by the grooves, it has heretofore been attempted to make the width of the longitudinal grooves wider or to arrange protrusions on the groove bottom of the grooves. However, the former method has the disadvantage that the wear resistance is decreased, and the latter method has the disadvantage that the drainage is decreased with the progress of the wear of the tread, so that the wet grip performance is decreased.
It is, therefore, an object of the present invention to advantageously solve the problem of stone-biting without causing a deterioration in the wet grip performance of tires.
A further object of the present invention is to provide a pneumatic tire having a tread pattern designed so as to prevent the grooves from biting small stones without lowering the wet grip pereformance of the tire.
These and other objects of this invention will become apparent from the description given hereinafter.